1. Technical Field
The present invention relates to a method of separating a secondary battery, and more particularly to a separation method in which a battery pack is disassembled to separate a normal secondary battery for re-forming a battery pack.
2. Background Art
A battery pack formed of a plurality of plate-like battery modules stacked in the thickness direction thereof is known as one type of power supply devices with a relatively large capacity for use in electric vehicles, hybrid electric vehicles, and so on. Such a battery pack has a compact size and a light weight and is therefore advantageous in that it can be mounted within a limited space in a motor vehicle. A battery module includes a plurality of cells arranged in a line, and each cell is a hollow rectangular parallelepiped shape casing made of a thin synthetic resin or metal containing therein battery containers for housing an electrolyte and an electrode member which form the secondary battery, respectively. While such a battery module is configured such that when the internal pressure of the battery container increases to a predetermined value or greater due to generation of hydrogen gas and so on within the battery container, for example, a safety valve is actuated to release the pressure within the battery container, there is a possibility that the battery module will expand in the thickness direction due to the rise of the internal pressure. Similarly, there is a possibility of expansion of the battery module in the thickness direction due to rise in the internal pressure at the time of over-discharge reaction, over-charge reaction, reduction in the gas absorption performance at low temperatures, and so on.
JP 9-120809 A discloses a structure in which a battery pack is sandwiched by a pair of end plates and the pair of end plates are then coupled to each other on the outside the battery pack by a pair of binding bands disposed along the stacking direction of battery modules.
Further, JP 2006-310309 A discloses a structure in which a spacer is provided between unit cells for retaining the unit cells and the spacers are configured to have different shapes in accordance with the positions of adjacent unit cells, so that the required strength of the spacers is secured, to thereby prevent deformation of the unit cells.
In addition, JP 2001-68081 A discloses a structure in which in order to couple coupling members and binding plates simply and with high operability without using a special jig, a screw mechanism is provided at an end portion of the coupling member, and coupling and separation of the coupling members and the binding plates is performed by the operation of the screw mechanism.
FIG. 10 illustrates a perspective view of an outer appearance of a battery pack of related art. A battery pack 21 includes binding plates (end plates) 23 on both ends of a stack of unit cells (battery modules) 22 in the stacking direction, the binding plates 23 being coupled together by binding bands 24 to thereby bind the unit cells (battery modules) 22 to form an integral unit. The binding band 24 is generally formed in a belt-like shape, and pairs of binding bands are disposed on a pair of opposing elongated side surfaces of the battery pack 21 at an appropriate interval such that the plate surface of the binding band 24 extends along the elongated side surface in contact therewith. The two end portions of the binding band 24 are fixed to the binding plate 23 by a rivet 25.
FIG. 11 illustrates a perspective view of an outer appearance of another battery pack of related art. A coupling member 5 has a rectangular cross section, and is of a plate shape such that the long side thereof is disposed vertically with respect to an elongated side surface of a battery pack 1. The coupling member 5 is configured such that a plane which is parallel to the flow direction of a cooling medium through which a cooling medium channel passes represents most of the outer surface. One end portion of the coupling member 5 is bent in an L shape with respect to the longitudinal direction of the coupling member 5 to form an L-shape attachment portion 5a which abuts against a surface of the binding plate 3 facing the unit cells (battery modules) 2, and the other end of the coupling member 5 includes an attachment plate portion 5b which extends in an L shape in the cross sectional direction of the coupling member 5 to abut against a peripheral side surface of the binding plate 4.
A fastening bolt 6 extending in the longitudinal direction of the coupling member 5 is inserted through the L shape attachment portion 5a, and a head portion 6a of the fastening bolt 6 is fixed by engagement. The fastening bolt 6 penetrates through a bolt hole formed in the binding plate 3, and a nut 7 which is threaded over this fastening bolt 6 from the tip end portion thereof is engaged with the binding plate 3 on the opposite side of the abut surface of the binding plate 3 with respect to the unit cells 2. The attachment plate portion 5b is fixed in a fastening manner to the binding plate 4 with an attachment bolt 8. Further, a positive electrode terminal and a negative electrode terminal 11 and 12 are projected at the upper end portions of both end surfaces of the unit cell (battery module) 2 in the longitudinal direction, and a safety valve 17 for releasing the pressure when the internal pressure of each unit cell (battery module) 2 is a predetermined value or greater, and a temperature detection hole 18 in which a temperature sensor for detecting the temperature of each unit cell (battery module) 2 is mounted, are formed.
When assembling the battery pack 1, the unit cells 2 are arranged in parallel and the binding plates 3 and 4 are disposed on both ends. Then, the fastening bolt 6 extending from the L shape attach portion 5a formed at one end portion of the coupling member 5 is inserted through the bolt hole formed in the binding plate 3, and the nut 7 is screwed over the fastening bolt 6 from the tip end side thereof, and the attachment plate portion 5b at the other end portion of the coupling member 5 is fastened and fixed to the binding plate 4 with the attachment bolt 8. Thereafter, the nut 7 is further screwed forward to urge the binding plate 3 against the unit cells 2 to achieve a predetermined binding state. Further, because a binding force due to an expansion caused by charging/discharging of the unit cells 2 and an increase in the internal pressure is applied to the load in the axial direction of the fastening bolt 6, with the fastening bolt having necessary strength, it is possible to assemble the coupling members 5 with a sufficient strength.
When disassembling the battery pack 1 at the time of maintenance and so on, the binding force can be released by gradually loosening the nut 7, which can eliminate the risk of damaging the binding plates 3 and 4 and the coupling members 5 as in the case of cutting the rivet.
However, conventionally, there has been no concept of disassembling the battery pack which is deteriorated in a safe manner and also reusing the secondary batteries (battery modules). While expansion of each secondary battery can be suppressed to a certain degree by sandwiching the secondary batteries with a pair of binding plates, in a case where a large number of secondary batteries are arranged, when a predetermined secondary battery expands, a pressure caused by such an expansion is absorbed dispersedly by compressive elastic deformation of other secondary batteries. The secondary batteries which have been used have different degrees of expansion and different expansion pressures within a battery pack. It is therefore important to reliably separate and effectively reuse the secondary batteries (battery modules) having remaining life, without impairing the performance of the secondary batteries.